1. Field of the Invention
This invention relates to a radiation image read-out apparatus, wherein a stimulable phosphor sheet, on which a radiation image has been stored, is scanned with stimulating rays, which cause the stimulable phosphor sheet to emit light in proportion to the amount of energy stored thereon during its exposure to radiation, the emitted light is photoelectrically detected, and the radiation image is thereby read out. This invention particularly relates to a radiation image read-out apparatus, wherein a stimulable phosphor sheet is held along a cylindrical surface and scanned with stimulating rays radiated from a rotating member, which rotates around the center axis of the cylindrical surface.
2. Description of the Prior Art
When certain kinds of phosphors are exposed to radiation such as X-rays, .alpha.-rays, .beta.-rays, .gamma.-rays, cathode rays or ultraviolet rays, they store part of the energy of the radiation. Then, when the phosphor which has been exposed to the radiation is exposed to stimulating rays, such as visible light, light is emitted by the phosphor in proportion to the amount of energy stored thereon during its exposure to the radiation. A phosphor exhibiting such properties is referred to as a stimulable phosphor.
As disclosed in U.S. Pat. Nos. 4,258,264, 4,276,473, 4,315,318, 4,387,428, and Japanese Unexamined Patent Publication No. 56(1981)-11395, it has been proposed to use stimulable phosphors in radiation image recording and reproducing systems. Specifically, a radiation image of an object, such as a human body, is stored on a sheet provided with a layer of the stimulable phosphor (hereinafter referred to as a stimulable phosphor sheet). The stimulable phosphor sheet is then scanned with stimulating rays, such as a laser beam, which cause it to emit light in proportion to the amount of energy stored thereon during its exposure to the radiation. The light emitted by the stimulable phosphor sheet when it is exposed to the stimulating rays is photoelectrically detected and converted into an electric image signal. The image signal is then used during the reproduction of the radiation image of the object as a visible image on a recording material, such as photographic film, on a display device, such as a cathode ray tube (CRT) display device, or the like.
Stimulable phosphor sheets are used as a means for recording radiation images mainly in the field of medicine, but they may be used in various other fields as well. For example, in U.S. Pat. Nos. 4,651,220 and 4,889,990, the applicant proposed novel methods for recording and reproducing an electron microscope image wherein a stimulable phosphor sheet is utilized. Basically, the proposed methods for recording and reproducing an electron microscope image comprise the steps of (i) exposing a stimulable phosphor sheet, which is capable of storing electron beam energy thereon, to an electron beam which has passed through a sample in a vacuum in order to store the electron beam energy on the stimulable phosphor sheet, (ii) thereafter exposing the stimulable phosphor sheet to, for example, stimulating rays which cause it to release the stored energy as emitted light, (iii) photoelectrically detecting the emitted light, an image signal being thereby obtained, and (iv) using the image signal during the reproduction of an electron microscope image of the sample.
It is desirable that a read-out apparatus, which is used for the aforesaid electron microscope image recording and reproducing methods in order to irradiate the stimulating rays to the stimulable phosphor sheet and to detect the light emitted by the stimulable phosphor sheet, be capable of scanning the stimulating rays at a higher density than the density, at which the read-out apparatus for the aforesaid systems for recording and reproducing the radiation image of a human body, or the like, scans stimulating rays. Also, it is desirable that the former read-out apparatus be capable of detecting the recorded images at a higher accuracy than the accuracy, at which the latter read-out apparatus detects the recorded images. In order to satisfy the aforesaid requirements, novel radiation image read-out apparatuses have been proposed in U.S. Pat. Nos. 4,886,968 and 5,047,643.
With the proposed radiation image read-out apparatuses, a stimulable phosphor sheet is held and secured along a cylindrical surface and scanned with stimulating rays radiated from a rotating member, which rotates around the center axis of the cylindrical surface. Basically, the proposed radiation image read-out apparatuses comprise:
i) a sheet holding means for holding a stimulable phosphor sheet along a cylindrical surface, PA1 ii) a stimulating ray source, which produces stimulating rays, PA1 iii) an optical element, which is located in an optical path of the stimulating rays, and which transmits one of the stimulating rays and the light emitted by the stimulable phosphor sheet and reflects the other thereof, PA1 iv) a spinner provided with: PA1 the spinner rotating the deflection mirror and the condensing lens together with each other and coaxially with respect to the center axis, the stimulating rays being thereby caused to scan the stimulable phosphor sheet in a main scanning direction, PA1 v) a sub-scanning means for moving the sheet holding means with respect to the spinner and in a direction parallel to the center axis, PA1 vi) a detection lens located in an optical path of the light emitted by the stimulable phosphor sheet, which light has passed through the condensing lens and comes from the optical element, the detection lens converging the emitted light, and PA1 vii) a photodetector for detecting the emitted light, which is converged by the detection lens. PA1 i) a sheet holding means for holding the stimulable phosphor sheet along a cylindrical surface, PA1 ii) a stimulating ray source, which produces the stimulating rays, PA1 iii) an optical element, which is located in an optical path of the stimulating rays, and which transmits one of the stimulating rays and the light emitted by the stimulable phosphor sheet and reflects the other thereof, PA1 iv) a spinner provided with: PA1 the spinner rotating the deflection mirror and the condensing lens together with each other and coaxially with respect to the center axis, the stimulating rays being thereby caused to scan the stimulable phosphor sheet in a main scanning direction, PA1 v) a sub-scanning means for moving the sheet holding means with respect to the spinner and in a direction parallel to the center axis, and PA1 vi) a photodetector located such that its light receiving face may be located at a position, at which the light having the center wavelength in the wavelength distribution of the light emitted by the stimulable phosphor sheet is converged by the condensing lens.
a) a deflection mirror, which reflects the stimulating rays coming from the optical element toward the stimulable phosphor sheet, the reflection being effected on the center axis of the cylindrical surface, and PA2 b) a condensing lens, which is located in the optical path of the stimulating rays having been reflected by the deflection mirror, and which converges the stimulating rays on the stimulable phosphor sheet, PA2 a) a deflection mirror, which reflects the stimulating rays coming from the optical element toward the stimulable phosphor sheet, the reflection being effected on the center axis of the cylindrical surface, and PA2 b) a condensing lens, which is located in the optical path of the stimulating rays having been reflected by the deflection mirror, and which converges the stimulating rays on the stimulable phosphor sheet, the condensing lens also converging the light, which is emitted by the stimulable phosphor sheet, at a predetermined converging position,
With the proposed radiation image read-out apparatuses, the stimulating rays can be converged to a spot having a small diameter, and therefore the aforesaid requirements can be satisfied.
However, with the proposed radiation image read-out apparatuses, the condensing lens is mounted on the spinner, and the detection lens for converging the light emitted by the stimulable phosphor sheet is located independently of the condensing lens. Therefore, the structures around the spinner and the photodetector cannot be kept simple, and the cost of the radiation image read-out apparatus cannot be kept low.
Japanese Unexamined Patent Publication Nos. 63(1988)-82410 and 64(1989)-6918 disclose apparatuses, wherein collimated stimulating rays are caused to impinge upon a condensing lens and converged on a stimulable phosphor sheet by the condensing lens. The light, which is emitted by the stimulable phosphor sheet when the stimulable phosphor sheet is exposed to the stimulating rays, is collimated by the condensing lens, and the emitted light which has thus been collimated is detected by a photodetector. With the disclosed structures, the detection lens described above need not be provided independently of the condensing lens. Therefore, it may be considered to utilize the disclosed structure in a radiation image read-out apparatus using a spinner and thereby to simplify the radiation image read-out apparatus and keep the cost of the radiation image read-out apparatus low.
However, in such cases, the emitted light which has been collimated is detected by the photodetector. Therefore, it is necessary to use a large-sized photodetector having a larger light receiving face than that of a photodetector used to detect the emitted light which has been converged. As a result, the size of the radiation image read-out apparatus cannot be kept small. Also, in such cases, if the distance between the stimulable phosphor sheet and the condensing lens fluctuates, the problems will occur in that the light emitted by the stimulable phosphor sheet diffuses from the collimated state, and therefore part of the emitted light goes to a position outside of the light receiving face of the photodetector. As a result, the emitted light cannot be detected accurately.